It is known to coat flexible supports (textiles) or solid supports using films or polymer coatings, for example silicones, preferably in the form of elastomers.
The silicone elastomer coatings on supports which are e.g. fibrous in nature, due to the intrinsic properties of the silicones, already provide numerous advantages for the composites thus formed, namely inter alia good flexibility and good mechanical strength.
Moreover, unlike standard elastomers, the silicones confer upon them inter alia improved high-temperature behaviour and a long life.
These characteristics are widely exploited in the uses of these coated fabrics for the production of airbags.
Thus, the patent FR-B-2.719.598 discloses silicone elastomer compositions which are cold vulcanizable (EVF) by polyaddition, for the coating of textile fabrics made of Nylon® intended for the production of “air bags”. These compositions include a mixture formed by:
(I) 25 w/w POS oil (MViDMVi): PolyDiMethylSiloxane—PDMS— α,ω (dimethylvinylsiloxy) with a viscosity of 100,000 mPa·s containing approximately 0.083% mol. of MVi groups ═(CH3)2(CH2═CH)SiO1/2, DVi=(CH3)(CH2═CH)SiO2/2;
(I′) 21 w/w PDMS MViDMVi (10,000 mPa·s), (SiVi=0.083% mol.),
(II) 5 w/w POS oil (MHDDHMH): poly(dimethylsiloxy)(methylhydrogenosiloxy) α,ω dimethylhydrogensiloxy, with a viscosity of 300 mPa·s and containing 0.17% mol. of H groups;
(III) Pt catalyst
(IV) 5 w/w adhesion promoter (VTMO/GLYMO/Ti(OBu)4;
(V) optionally a mineral filler,
(VI) 0.03 w/w EthynylCycloHexanol
(VII) 38 w/w POS vinyl resin=MViDDViMViQ (SiVi 0.6% by weight).
VTMO vinyltrimethoxysilane
GLYMO gamma-Glycycloxypropyltrimethoxysilane
Bu: butyl
Nevertheless, it is known that the layers of elastomer silicone coating often have a slightly tacky feel which is disadvantageous for “airbags”. This concern for surface slipperiness also applies to coatings for thermal-transfer ribbons (e.g. made of polyester) or also protective wrapping films (e.g. made of polyethylene or polypropylene).
Thermal-transfer ribbons can be used in thermal-transfer printers. These thermal-transfer ribbons are very thin (a few microns) and are coated, on one of their surfaces, with a layer of ink (waxes or resins) and on the other surface, with a protective coating. A very thin protective coating, with a thickness comprised between 0.1 and 1 micrometer is generally used in order to protect the surface of the film and improve the impact of the printing head without deforming the transfer of the ink onto the applied support. In printers whose printing speed is between 150 and 300 mm/s, it is very important for the printing head (flat or wedge-shaped), when it strikes the protective coating of the ribbon, to slide on the surface of the coating, at a high temperature of between 100 and 200° C.
As regards protective wrapping films, it is sometimes envisaged to apply a silicone-based top varnish to them in order to confer anti-adhesion properties on them. However, it is advisable for this top varnish to possess a slipperiness which is at least equivalent to that of the starting plastic film (printed or otherwise).
In all the cases mentioned above by way of illustration, the composites suffer from a lack of slipperiness, which can be associated with mechanical and surface properties (too high a coefficient of friction) of the silicones.
In the case of textile applications, this drawback of a lack of slipperiness is manifested in practice by a low of mobility of the coated fabrics on the work tables which is detrimental to productivity. More specifically in the case of airbags, it is the deployment of the bag during the release of the airbag which can be slowed down in a very harmful manner.
Various types of treatments can be envisaged in order to remedy this difficulty. Nevertheless the compromise between surface slipperiness and properties of use is such that varnishing seems to be one of the means most suited to this purpose.
In the field of architectural textiles or furnishing textiles, manufacturers are moreover requesting “(woven or non-woven) fibrous support/elastomer coating” composites which possess not only the essential characteristics mentioned above, but also significant additional performances such as:
a resistance to fouling,
good appearance characteristics in particular with the regard to colour and gloss,
suitability for spreading on a silicone, or even non-silicone layer (for example Vinyl PolyChloride, Polyurethane, PolyAmide),
easy and economical utilization on an industrial level,
and good cohesion of the composites.
These properties can be provided by an appropriate surface coating (varnishing).
The general problem on which the invention is based is therefore the development of a silicone varnish suitable for perfectly fulfilling this role, in particular with respect to anti-fouling properties.
The PCT Application WO-A-00/59992 (R99035) describes silicone compositions which are useful in particular for producing varnishes which can be applied to supports, the coefficient of friction of which it is sought to reduce. One of these compositions comprises at least one polyorganosiloxane A (POS) which can be cationically and radically cross-linked using functional cross-linking groups (FCG) and a primer C chosen from onium borates, characterized in that it also comprises POS D molecules which are substituted by secondary functional groups (SFG) carried by silicon atoms and selected from those that include at least one alkoxy and/or epoxy and/or carboxy motif and optionally a filler (e.g. silica).

These compositions can moreover comprise fillers and in particular silica fillers which can be for example:
combustion silicas treated with hexamethyldisilazanes or octa-methylcyclotetrasiloxane (specific surface area up to about 300 m2/g), fumed silicas, ground synthetic or natural (polymer) fibres, calcium carbonates, talc, clays, titanium dioxides, etc.
Such compositions are used as anti-fouling varnishes for RTV silicone coatings for airbag fabrics, heat transfer ribbons or packaging films.
Such varnishes are not among the most effective in terms of anti-fouling properties and remain capable of improvement in terms of their coefficient of sliding friction. Moreover, they require the use of particular silicones crosslinkable by a cationic method under UV activation, which allows a margin of improvement from the economic point of view and from the point of view of simplification of the means utilized.
The Application PCT WO-A-WO 03/106564 describes an anti-friction silicone varnish for textiles coated with silicone elastomers. This economical, adherent varnish, providing the sought slipperiness, which is resistant to fouling, and glossy, is formed by a silicone composition cross-linkable by polyaddition comprising, on the one hand,
85 parts of PDMS containing approximately 2.5% of Vi in the form of DVi groups
15 parts of PDMS α,ω-diMeVi with a viscosity of 600 mPa·s
20 parts of PDMS α,ω diMeVi with a viscosity of 100 Pa·s
0.052 parts of ethynylcyclohexanol
10 parts of γ methacryloxypropyltrimethoxysilane
15 parts of polymethylhydrogensiloxane with a viscosity of 20 mPa·s
0.1 parts of platinum catalyst
5 parts of a particulate component (D), namely Orgasol® 2002 ES3 (PA 12 powder with an average diameter of 30 μm).
The Patent Application WO-A-2004067613 discloses another silicone varnish for anti-fouling coating of silicone composites. This varnish comprises a composition of functional silanes which cross-link under the action of atmospheric humidity said crosslinking being accelerated when hot. This composition is, for example as follows:
Alkenylsilane-A.1-: Vinyltrimethoxysilane (VTMO),
Alkenylsilane-A.2-: Dynasilan® 6490 is a condensate of vinyltrimethoxysilane (VTMO) marketed by Degussa,
Component-B.1- of the catalytic system: DADBE: dibutyltin diacetate,
Component-B.2- of the catalytic system: TBOT: butyl titanate,
Ultrafine filler-C-: R812 is a treated pyrogenated silica marketed by Degussa.
The Patent Application WO-A-2004067620 also discloses another anti-fouling silicone varnish for textiles coated with silicone elastomers. This economical, adherent, non-slip and glossy varnish comprises a cross-linkable silicone composition based on, per 100 parts by weight:
1—at least 80 parts by weight of:

2—from 0.1 to 10 parts by weight of:

3—from 0 to 10 parts by weight of at least one polydimethylsiloxane (PDMS) acrylate or epoxy;
4—from 0 to 10 parts by weight of at least one silylated compound as defined above and carrying, per molecule, at least one epoxy group;
5—from 0 to 10 parts by weight of at least one PDMS acrylate/epoxy;
6—from 0 to 10 parts by weight of at least one ultrafine filler as defined above;
7—from 0 to 10 parts by weight of at least one thickening agent as defined above;
8—from 0 to 10 parts by weight of at least one other functional additive as defined above.
These last two varnish compositions are very effective but can in certain cases exhibit a few defects in their advantages; in particular their method of cross-linking means that they are very sensitive to the environment in which they are used (humidity, light) which can make them difficult to use in textile-coating machines.